53 



udvildingeii ond ellers. Jeg benytter derfor min tidligere 

 difiuitiou og skal siden komme til dets fysiologiske syns- 

 punkt, livorfra ogsaa kimbladeiie kan Letragtes. 



Betragter vi nu med denne definition for oie den i 

 dette arbeide tidligere beskrevne udviklingsproces, saa maa 

 man IVemforalt holde den emliryonnle og knopudviklingen 

 ud fra liinanden. ]\line undersøgelser over den emhi-i/onaJc 

 udvikling forte til en liekræftigelse af de ældre med den 

 ,,erfaringsmæssige kimbladlov- overensstemmende resultater, 

 og frembyder dei-for intet af interesse for kimbladlæren. 

 Ligeledes paaviste jeg, at det var uoverensstemmende med 

 al erfaring, naar Pkon mener, at et organ, som peribran- 

 clualsækken hos en familie kan udvikle sig fi'a entodermen 

 (Botrylhis) og lios andre familier fra ektodermen. Frem- 

 foralt iuevdede jeg. at det var begrebsmodsigende at anfore 

 et saadant forhold som stotte for kimbladlæren. 



Anderledes forholdt sig imidlertid knopudviklingen. 

 Her viste det sig dels at knopanlæggets ..indre blære" snart 

 kan anlægges fra entodermen, snart fra ektodermen, dels 

 ogsaa, at organerne under denne udviklingsproces anlagdes 

 efter en anden lov (en anden formudrll']/ii(/) end under den_ 

 embryonale udvikling. Dette forte mig imidlertid allerede 

 tidligei'e (31 ) til at betragte det materiale, hvoraf knop- 

 perne dannes som udifferentieret materiale, der hos en 

 familie kunde forefindes i et ektodermalt, hos en anden 

 familie i et entodernualt organ. At dette er noget lievis 

 mod kimbladlæren i den forstand, som vi ovenfor iiar ud- 

 viklet den, kan jeg ikke forståa. Kiml)ladlæren omhandler, 

 hvorledes individet bygges op under den embryonale udvik- 

 ling. Mine resultater lærer altsaa alene, at der under den 

 embryonale udvikling kan bevares udifferentieret materiale 

 og det i begge kimblade. men om organernes dannelse i 

 denne udviklingsproces forovrig lærer de intet nyt af theo- 

 retisk betvdnina'. 



I)ei' tindes imidlertid ogsaa andre kimbladlrerer end 

 den. jeg bidtil har behandlet, og som var et umiddelbart 

 resultat af den udviklingshistoriske erfaring. 



Man iiar forsogt at forklare den almindelige lov for 

 kimbladenes udvikling dels ud fra udviklingsmekaniske, dels 

 ogsaa fra fylogenetiske synspunkter. I dette kapitel skal 

 vi alene i korthed omtale de udviklingsmekaniske kimblad- 

 theorier, specielt da den af We/sviaiin forfægtede mosaik- 

 theori og den af Driesch. Heriuig og Wilson udviklede 

 evolutionistiske epigenesistheori. Det ligger udenfor arbei- 

 dets ramme at give nogen indgaaende lielysning af disse 

 theorier, min opgave vil alene være den ved hjælp af dem 

 at belyse mine egne specielle resultater. 



Driescli karakteriserer den Weisuiaiiitsl;e theori i føl- 

 gende ord (IG, pag. 3j: ..Einer der -vvesentlichen Elemen- 

 tarprocesse, ^velche die Entwicklung eines lebenden "Wesens 



more difficult than before, to describe the developuuMit- I 

 therefore make use of the former definition. and will sub- 

 se(iuently come to the piiysiological point of view from 

 which the geiun-layers may also be regarded. 



If now. keeping this detinition in view, we consider 

 tlie jirocess of development previously described in this 

 paper. the embryonic and tiie bud development must first 

 of all be kept distinct from one another. Jly investiga- 

 tions of the emhri/onic development led to a confirm;ition 

 of the earlier results that harmouised witii the ,.em])irical 

 germ-layer law", and tlierefore offer nothing of any intei'est 

 to the germ-layer theory. I also showed that PiiouH 

 theory that an organ like the peribrauchial cavity eau 

 develope in one family (Bdinjlhis) from the endoderm, and 

 in another family from tlie ectoderm, was contrary to all 

 esperience. Above all, I maiutained that it was a con- 

 tradiction of ideas to bring forward such a circumstance 

 in support of the germ-layer theory. 



The case was otherwise, iiowever, witli bud develop- 

 ment. It tliere appeared, jjartly that the iniier vesicle of 

 the rudimentary bud can sometimes originale in the endo- 

 derm, and sometimes in the ectoderm; and partly too. that 

 in this developmeutal process, tlie organs commenced to 

 form according to another law (another form-åevélopment) 

 than in the embryonic development. This had already led 

 me (31) to consider the material from which the l)uds are 

 forined as undifferentiated material, which in one family 

 can hv met with in an ectodermal organ, in anotiier family 

 in au endodermal organ. I cannot see that this is any 

 proof against the germ-layer theory in the sense in which 

 we luwe propounded it above. Tlie germ-layer tlieory treats 

 of the building up of the animal in the embryonic develop- 

 ment. My conclusions too, only teach that during the 

 embryonic development, undifferentiated matei-ial can be 

 preserved, and that in both germlayei-s ; but concerning the 

 formation of the organs in this developmeutal process. they 

 teach no new thing of theoretical importance. 



There are. iiowever. also other germ-layer theories 

 than that of wliicii I have up to the present treated, and 

 which was an immediate result of developmental-historical 

 experience. 



An atterapt has beeu made to explaiii the general 

 law for the development of the germ-layers, starting partly 

 from developmental-mechanical, partly from phylogenetical 

 points of view. In this ciiapter we will only brieffy meii- 

 tion the developmental-mechanical germ-layer theories, parti- 

 cularly the mosaic theory contested by Wcismann. and the 

 evolutionary epigenesis theory propounded by Driesch, Hert- 

 uig and Wilson. It does not come withiu the scope of 

 this paper to give any detailed information concerning these 

 theories; and my aim will only be by their aid to tlirow 

 light on my own particular results. 



Driescli characterises the Weismann theory in the 

 followiug words (IG. p. 3): „Einer der wesentlichen Ele- 

 raentarprocesse, welche die Entwicklung eines lebenden 



